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Chapter 7: Using The Compressor
DN540
26 Operator Manual
Simple compression (auto mode)
For many every day compression jobs an RMS compressor with automatic time
constant set up (attack and release) is the best solution, providing quick and easy set
up. The RMS compressor slows the time constants on relatively steady state signals,
reducing distortion and pumping, and when large signal changes occur they
automatically speed up, capturing and constraining the bulk of any large sound level
variations.
Very often, combining the automatic time constant adjustment with ratio and threshold
is all you need to set up a good sounding compression. The DN540 auto compressor
operates in exactly this way, providing simple fast set up on straight forward
compression jobs.
Advanced compression (manual mode)
RMS compressors are not fast enough to capture everything on transient material
because the averaging process always adds some delay; thus they are not suitable for
ultimate protection against system overloads etc. Also, their creative use to tailor
percussive instruments is very threshold dependent and often results in attacks that are
either too fast or too slow for the desired effect (unless the sound source is extremely
regular, which is not typical with most musicians).
For more difficult compression duties a compressor with fully adjustable attack and
release is a better choice. With this style of compressor there is no averaging process
delay, so that the action of attack or release can start the instant there is a change in
signal amplitude that requires it. The user must define the rate of response and can
adjust this precisely to match the sonic effect required on the source material.
Normally, this also results in high distortion on constant signal levels because the
compressor attacks and releases on every cycle, but advanced compressors utilise
windowing methods whereby the time constants set are greatly increased on steady
state material. Another technique used is to automatically apply a little hold before any
release commences.
The above techniques are integral to the semi-linear attack and second order release
characteristics of the DN540 normal mode compressor.
Linear attack provides a constant rate of attack (in dB against time) such that large
changes in programme signal level take a little longer to compress than smaller ones.
However, on material with more constant signal levels the attack rate of the DN540
manual mode compressor automatically reduces. This appears as a curvature in the
linear attack rate characteristic as it nears completion, hence the term “semi-linear”.
This makes the compression very transparent providing some dynamic control, but
without unduly affecting the intentional dynamic content of the source material.
This type of compression can be used on difficult instruments, such as acoustic guitars,
with slower attack time settings and relatively fast release to keep an equal perceived
loudness within a mix without producing excessive amplitude flutter or distortion. It
can also be used with faster attack times to capture dynamic instruments like electric
bass guitar without adding excessive distortion on constantly compressed passages.
Adding soft knee noticeably delays the onset of attacks, which can be particularly useful
on drums where compression can be applied to emphasise transients giving more
punch while retaining a good deal of artistic dynamic from the drummer.
Thus, when suitably adjusted the manual compression mode is suitable for any task,
such as to capture fast transients in order to provide system protection, producing
subtle compression of dynamic range without changing timbre or removing intentional
accents made by the artiste or to deliberately thicken transient sounds.